Silent wave radio transmission system



May 26,1931. E. E. CLEMENT 1,807,510

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Patented May 26, 1931 UNITE :5;

. EDWARD E. CLEMENT, OF WASHING-TON, DISTRICT OF COLUMBIA, ASSIGNOR T EDWARD F. COLLADAY, OF WASHINGTON, DISTRICT OF COLUMBIA SILENT WAVE RADIO TRANSMISSION SYSTEM Application filed August 7, 1926. Serial No. 127,898.

My invention relates to the transmission of intelligence, including certain'aspects of electrical transmission of energy both through or over wires, and by means of high frequency wave radiation. The object of the invention is to provide what I have chosen to call secret wave or silent wave transmission, which, while useful in any transmission system, will find a particularly important use in the system which I have chosen to call the radiowire system of broadcast distribution, described and claimed among others in my prior co-pending application, Serial No. 746,357, filed October 28, 1924. (File 4325).

The present invention is in the nature of an improvement over those disclosed in the following applications: Serial No. 31,928, filed May 21, 1925; Serial No. 63,977, filed October 21, 1925; Serial No. 65,860, filed October 30, 1925; Serial No. 65,861, filed October 30, 1925.

In order to attain my object, I resort to two phase or polyphase wave transmission,

" both over wires and by radiation. In my prior co-pending application, Serial No. 63,-

977, above mentioned, I have disclosed a scheme of double modulation, wherein a primary carrier wave has modulated upon it two different secondary or intermedlate frequency carrier waves, and these two IF waves, carry, respectively, audio modulations which are rendered audible in an authorized receiver by phase adjustment, but which neutralize each other in any other receiver. In the other two applications mentioned, Nos. 31,928 and 65,861, other methods of transmission, involving phase displacement and phase adjustment, are described.

In the present case I go farther than in any of the other applications, and use the polyphase transmission not only in order to secure secrecy, but also to enable selection of program to be made without multiplying frequencies. Where the several phases in a polyphase transmission system are symmete rical in relation to each other, as in a twophase or a three-phase system, with phases 180 or 120 apart, it canbe shown that the algebraic sum of the energy values in the two or the three phases, respectively, at any given instant, is equal to zero. I take advantage of this by transmitting diiferent programs on the several phases of trans mitted current of the same frequency, whereby ordinary instruments, receiving all the phases in one input circuit, will either remain silent so far as any modulations are concerned, or will reproduce a mixed and unintelligible sound. By means of an analyzer, using the homodyne principle, I have discovered that the separate modulated phases may be separately received and detected.

In one simple form, this system involves I the generation, for example, of two phase current, with the phases 180 apart, a separate modulation of eachphase, and their transmission over a wire transmission circuit. Since the sum of the unmodulated energy waves in the two phases at any given instant is equal to zero, the unmodulated carrier current may be supposed to cancel out, leaving only two bands of frequencies each composed of the carrier frequency in one phase plus or minus the frequencies modulated upon it, and each carrier frequency component ofeach side band being 180 dephased from the other. Any one seeking to receive signals of this kind with an ordinary receiver will get either nothing or a mixed jumble. On the other hand, by homodyne receiving,'with a two phase receiver in which the receiving oscillator supplies two opposite currents of the same frequency which may be brought into synchronism with either of the two phases of the transmitter, either of the two carrier currents with its modulations transmitting station, will enable the two side bands or two separate phases to be separately received, by analysis, and separately detected to give up their modulations selectively.

The last form to be mentioned in a modification of that disclosed in my prior application hereinbefore referred to, using double modulation, and employing dephased modulated IF waves for the purpose of neutralizing and cancelling out the signals in an unauthorized receiver, while enabling them to be received, selected, and detected, in an authorized receiver.

It is to be understood that both single and double modulation are contemplated in so far as each of them is applicable in each one of the several aspects of this invention. It is also to be understood that the two phase circuits herein shown and described, while they have all been reduced to practice, are used for convenience only, and simplicity of disclosure. The same principles and arrangement broadly, have been embodied in three phase circuits, both for wire transmission and for radiation, and the same results can be attained thereby. If anything, a better balance can be obtained with three phase than with two phase transmission, and of course this gives a wider range of program selection, as well as a closer approximation to the silent wave. The three phase system will be presented and claimed as such in a separate application.

My invention is illustrated in the accompanying drawings, in which Fig. 1 is a circuit diagram of the invention applied to a duplex system for transmission over wired lines.

Fig. 2 is a modification in which a single pair of oscillator coupler coils are used.

Fig. 3 is a modification of the arrangement of Fig. 2 in which the signal modulations are transmitted by radio while homodvne oscillations are transmitted by wire.

Fig. 4 is a rearrangement of the transmitter circuits of Figs. 2 and 3 to more clearly bring out the symmetry of the circuit connections. 7

Fig. 5 is a modification in which the signal currents are transmitted by radio and the homodyneoscillations are generated at the receiving station.

Fig. 6 is a modification in which the unmodulated radio frequency oscillations for both the transmitter and receiver are derived from common or base low frequency oscillations supplied to both transmitter and receiver over a wired circuit.

Fig. 7 is a modification in which the un modulated signal carrier current is transmitted by wire to the receiving station to supply homodyne current and is transmitted by radiation from the transini ter after modulation by double modulation.

Fig. 8 is a modification in which the signal currents and the homodyne currents are supplied each over one of a pair of grounded line circuits.

Fig. 9 is a modification in which the signal currents are transmitted over a pair of line wires while the homodyne currents are transmitted over circuits including both line wires and ground and balanced as to the line circuit.

Referring to the drawings in detail, and first to Fig. 1, 1 and 2 are the thermionic triode tube modulators arranged with their input circuits 3 and 4: coupled through Variable coupling coils 5 and 6, respectively, with the oscillation supply circuit 8 to which high frequency oscillatory currents are supplied through the usual coupler coil 10 from an oscillator 9 which oscillator is here shown as a thermionic tube oscillator of a type well known and understood by those skilled in the art, and so need not be described in particular. The modulator tube input circuits 3 and l are connected with the secondary windings of modulation input transformers 11 and 12 whose primary windings are connected in circuit with the transmitters or microphones 13 and 14:, respectively. The microphones 18 and 14 are provided with suitable sources of current such as the batteries 15 and 16 respectively. To offset the impedance of the transformer secondary windings these are shunted with by-pass condensers 17 and 18. The output or plate circuit of the modulator tube 1 includes, in series, the source of plate current 19 and the primary winding of a variable coupler 20 while the output circuit of the modulator tube 2 similarly includes the source of plate current 21 and the primary winding of a variable coupler 22. The secondary windings of the couplers 20 and 22 are connected in series in the line 23-24 through a pair of condensers 25 and 26, one condenser in each line. This line 2324 extends over an indetermediate distance, indicated by the dotted line extension, to a receiver 27 where it is connected to the terminals of the pr'- mary winding of the pick-up coupler 28. This receiver comprises in its simplest form, as shown, a detector tube 29 whose input circuit includes the secondary winning of the pick-up coupler 28 and the secondary winding of the oscillator coupler 30 connected in series, while the output circuit includes the usual source of plate current 31 and signal indicator or receiver 32. The primary winding of the oscillator coupler 80 is connected through a pole-changer switch 33 to the oscillation supply circuit 8 which also extends from the transmitter to the receiver through the indeterminate intervening distance as indicated by the dotted line extension.

In operation, the various tubes are energized or set in operation and the variable couplers 5 and 6, 20 and 22, and 28 and 30 are adjusted until the different sets of signals picked up by the microphones 13 and 14, respectively, may be selected, one to the exclusion of the other by throwing the polechanger switch 33 to one side or the other to supply the oscillations derived from the circuit 8 to the input circuit of the detector 29 in one or the other of opposite phase. This condition when obtained will continue enabling any one set of signals to be selected to the exclusion of the other at the receiving set 27 WVhile only one receiver 27 is shown in the system as diagrammed in Fig. 1, for the sake of simplicity of disclosure, it is to be understood that in practice the output of the modulator tubes 1 and 2 and the oscillations supplied by the oscillation supply circuit 8 will be transmitted over a number of different lines similar to 23 and 24 and the extension of circuit 8 to a number of receiving sets 27 Such multiple connections may be connected in any known or other suitable manner such as simple or multiple branch circuits from the lines 23 and 2% and 8, multiple inductive coulping with the output circuits of the tubes 1 and 2, the oscillator 9, etc., with or without any desired number of interposed stages of amplification. It is also to be noted that the modulator circuits may be elaborated to increase the power and the quality of modulation in any known or other suitable manner without changing their functions in a system.

The system diagrammed in Fig. 2 is'the same as that of Fig. 1 except that input circuits of the modulator tubes 12 have been changed to enable the use of one oscillation coupler 34 instead of two couplers such as 56 of Fig. 1. This enables the phase relation of the carrier current oscillations in the modulator input circuits to,

be maintained constant irrespective of the degree of coupling between the windings of the coupler so that this coupler may be a fixed coupler thus doing away with one adjustment in the transmitting circuit. Another and very slight difference between Fig. 2 and Fig. 1 is that the receiving set27 is provided with a tuning condenser 35 connected across the terminals of the primary winding of the pick-up coupler 28. The remaining apparatus elements and circuit connections are the same here indicated by the.

same reference numerals as those of Fig. 1.

In the operation of the circuit arrangement of Fig. 2, the coils 20, 22, 28 and 30 are adjusted until either one of the sets of modulations picked up by the microphones 13 and 14 may be selected at the receiving set 27 by throwing the pole-changer switch 33 to one side or the other.

The system diagrammed in Fig. 3 is the same that of Fig. 2 except that the modulated waves or electricalvariations carrying the-signals are transmittedto the receiving set by radiation. The only circuit changes necessary to effect this consists in the opening of t e line 2324 to connect the conductors 23 and 24 to a radiating antenna and 'counterpoise and to connect the pick-up or input circuit of the receiver 27 to a receiving antenna 36 which may be a loop as shown or any other known or suitable form of pick-up device. The-operation-of the system shown in Fig. 3 is'similar in all respects to that of Fig. 2.

The circuit diagram of Fig. 4. is a rearrangement of the circuit of the duplex transmitter of Fig. 2 to bring out the electrical symmetry of the circuit and aid in the interpretation of the more conventionalized circuit diagrams which follow.

As a common carrier wave is used for both modulators before it is given a double or duplex use, the two forms or circuits in which it is used for the two different sets of monulations are referred to as No. 1 phase and No. 2 phase, and the two sets of modulating apparatuses referred to. as No. 1 phase modulator and No. 2 phase modulator. I

In the succeeding diagrams of Figs. 5, 6, '7 and 8, the rectangles labelled No. '1 phase mod. are supposed'to contain the apparatus enclosed in the upper dotted line area of Fig. 4, while those labelled No. 2 phase mod. are supposed to contain the apparatuses enclosed in the lower dotted line area of Fig. 4:.

The system diagrammed in Fig. '5 is the same as that of Fig. 3 except that an open or wire antenna38 and antenna coupleri'39 are used instead ofthe loop antenna and the reproduced or resupplied carrier-current oscillationsare generated at the receiver 27 by local oscillator 40. The operation of this arrangement is the same as that of the preceding arrangements except that the oscillator 40 must first be carefully adjusted to the frequency of the original carrier wave'before adjustment of the oscillator'coupling coil. Fig. 6 is the same as that of Fig. 3 or Fig. 5 except thatthe oscillations of carrier frequency for both the transmitter and the receiver arederived from low frequency oscillations transmitted over a Wire line. Means for deriving the relatively high frequency carrier current oscillations from the wire-transmitted low frequency currents is here shown as consisting of harmonic producers which, of course, it is to be understood are to be adjusted so as to produce in their output circuits oscillations of the same frequency. The phase is a little less important as this may be adjusted in degrees by adjustment of the oscillation coupler of the receiving set and reversed by operation of the pole-changer switch, after such adjustment. It is also to be noted that in place of the harmonic producers, other forms of frequency changers or frequency multipliers may be used.

The arrangement of Fig. 7 is the same as that of Figs. 5 and 6, except that the signal transmission is by means of double modulation in which the signal modulating carrier current is of an intermediate frequency capable of being transmitted over wires but is transmitted, after modulation, as modulations on a radio frequency carrier and transmitted by radiation. With this arrangement, as the carrier current is of an intermediate frequency, capable of wire transmission, it may be supplied to the receiving set by transmission over a wired circuit 8 like that of Figs. 1 and 3.

The arrangement of Fig. 8 is identically the same as that of Fig. 2 except that the two conductor line circuit 232& and 8 are substituted by single conductor grounded circuits.

Fig. 9 is a fragmentary circuit diagram showing the arrangement of Fig. 2 with the two wired circuit 8 substituted by a grounded phantom circuit &1, balanced on the line circuit 23-2et hat I claim is:

The method of continuous wave multiplex transmission of signals which consists in modulating each of a plurality of high frequency undulatory carrier currents with a different relatively low frequency undulatory signal, transmitting the carriers thus modulated simultaneously in such manner that the sum of the unmodulated portions of said carrier waves will be equal to zero, conveying one or more dephased undulatory carrier currents of the same frequency as the original carrier currents from the point of origination to the receiving point over a separate medium from that utilized for the transmission of the modulated waves, receiving the side bands representing the modulated portions of the carriers upon separate receiving circuits, supplying said dephased undulatory carrier currents to said circuits for homodyne receiving, adjusting the phase of each of said homodyne currents to bring it into exact phase with one of the modulated carrier waves received, combining said current with the received side band, and detecting and rendering audible the signal on the completed modulated carrier thus produced in each receiving circuit.

In testimony whereof I hereunto afiiX my signature.

EDWARD E. CLEMENT. 

